A situation we are in, an activity we are engaging in, a substance we are imbibing, all can put us into a mental or physical state; when we leave that situation behind us, or stop doing the activity, or stop imbibing the substance, we still feel its effects even as we begin to emerge from the situation or state. That residual effect as we gradually leave it behind or emerge is called coming off (of) it.
She's just coming off of a bad marriage and doesn't want to date yet.
She's just coming off a three-week vacation and resents being back at work.
She's just coming off a long shift at the hospital and is very tired.
She's just coming off a bad LSD trip and is still hallucinating.
She's just coming off a bender and has a bad hangover.
She's feeling some nausea. She's coming off the scopolamine they gave her after the surgery.
The president is coming off of a party Congress where he was elevated to the status of the most powerful leader.
The president is still feeling the residual effects of having been elevated to the most powerful leader at the party congress.